The present invention relates generally to sensing electrical current on a current path, and more specifically, to calibrating a current sensor by trimming target surfaces along the current path.
Many products require sensing electrical current in a current path to provide the necessary input for electronic control devices. The accuracy of the current sensing and current measurements may be affected by variations in resistance at the current path, variations at jointed areas, even material changes in grade and density of the conductor material. The sensor itself may introduce errors contributing to inaccuracies. For example, when using a current transformer (CT), inherent variations from one CT to another can affect the transformer""s accuracy. Consequently, variations with respect to different CTs necessitate setting tolerance parameters to accommodate these variations.
In circuit breaker applications, the current is measured by installing a CT that is directly affected by the current flow through the conductor. The electrical current may be measured by passing only a portion of the current through the CT or by passing all of the current through the CT. A portion of the current may be measured as representative of the whole current. To measure a portion of the current, a current bridge or current divider may be used.
Current dividers and current bridges enable one to determine the magnitude of a large current by dividing the current into parallel flows, and measuring only a fraction of the total current, i.e., by measuring the current through one branch of the conductor. The current measurement is then divided by the fraction of current through that conductor branch to determine the total current in all parallel conductor branches.
Current dividers are a useful means of measuring a large current or current through large conductors, however they have not greatly overcome the inherent inaccuracies of current sensors discussed above.
Therefore, it is desirable to calibrate current sensors to overcome the manufacturing variations in conductors, sensors, and associated electronics.
The above discussed and other drawbacks and deficiencies are overcome or alleviated by a method for calibrating a current sensor having a conductor that comprises at least two conductor branches electrically connected in parallel. The method comprises passing a predetermined electrical current through the conductor, measuring a fraction of the current that passes through a measured conductor branch, which is one of the two conductor branches, comparing the measured current against a predetermined target current, trimming a calibrating conductor, which is one of the at least two conductor branches, the trimming taking place when said measured current and said predetermined target current are not equal.